OPINION:
They are trying to argue retention of the current definition of marriage on the basis that it's been extant for a long time.

That reasoning is seriously flawed.

All tradition and custom have a starting point, albeit often from long ago.

The implication is, therefore, that because there was a starting point, there can also be an end point.

Tradition and custom of all kinds aren't inviolate - they change over time in line with changed cultural norms.

Slavery is a good example.

It's not long ago that several countries were certain slavery was ordained by God and justified in Christian scripture.

The idea, also, that a wife was her husband's property was a commonly accepted ''norm'' at one time.

It is no longer - in most liberal societies, anyway.

So the fixed views of Family First and the Conservative Party, being well out of date with now accepted views of social justice, can safely be ignored. Support for the so-called gay-marriage Bill won't be the end of society.

It's simply one more step along the way to a more caring and just society.